This application is related to Japanese Patent Application No. 2001-10680 filed on Jan. 18, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a link mechanism constructed by plural links, which is suitably used for a fluid passage switching device such as an inside/outside air switching device of a vehicle air conditioner.
2. Description of Related Art
In a conventional link mechanism for a fluid passage switching device of a vehicle air conditioner described in JP-Y2-1-26494, a cam groove having a predetermined shape is provided in one side link, and a pin sliding in the cam groove is provided in the other side link, so that driving force of a driving source such as an electrical motor is transmitted to a driven unit. Because ram pressure is applied to the inside/outside air switching device while the vehicle is running, a switching door is need to be pressed to an outside air introduction port while crushing a packing for closing the outside air introduction port. Accordingly, when an area of the outside air introduction port increases, a closing force and a closing amount of the switching door are increased.
On the other hand, in this link mechanism, the cam groove is bent to have a predetermined radius of curvature. However, when the radius of curvature is made smaller in a bent portion of the cam groove, a pin sliding speed increases in the bent portion, and therefore, a relative large collision noise causes when the pin collides with a side surface of the cam groove. Here, a shock absorbing mechanism (buffer mechanism) may be provided in a collision position within the cam groove. However, in this case, the shape of the cam groove becomes complex, and a product cost of the cam groove increases.
In view of the foregoing problems, it is an object of the present invention to provide a link mechanism which reduces a noise due to a collision between a pin and a side wall defining a cam groove, while a product cost of the cam groove is restricted.
According to the present invention, in a link mechanism for transmitting a driving force from a driving source to a driven unit, a first link is disposed to be movable by the driving force from the driving source, a second link is operatively linked with the first link in a connection portion to move the driven unit. In the connection portion, one of the first link and the second link includes a first cam groove having a bent portion which is bent by a radius of curvature smaller than a predetermined value, and the other one of the first link and the second link includes a first pin slidable within the first cam groove. In the link mechanism, the first pin is disposed to be slidable in the first cam groove with a sliding speed, the sliding speed of the first pin is set lower when the first pin slides within the first cam groove by a predetermined amount, as compared with the sliding speed before the first pin slides in the first cam groove by the predetermined amount. Accordingly, a collision energy between the first pin and a side wall defining the first cam groove can be made smaller without providing a shock-absorbing mechanism in the first cam groove. Therefore, a collision noise due to a collision between the first pin and the side wall of the first cam groove can be reduced while the first cam groove is manufactured in low cost.
Preferably, the sliding speed of the pin is set lower when the first pin enters into the bent portion, as compared with the sliding speed before the first pin enters into the bent portion. Therefore, the collision energy of the first pin with the side wall of the first cam groove can be made smaller in the bent portion, and the collision noise can be further reduced. Here, the state when the first pin enters into the bent portion includes an approximate twice range of the radius of curvature on an outer side of the bent portion.
The link mechanism includes a third link driven by the driving source to drive the first link, and the third link is operatively linked to the first link. In a connection portion between both the first and third links, one of the first link and the third link includes a second cam groove, and the other one of the first link and the third link includes a second pin slidable within the second cam groove. The second cam groove has first and second operation groove parts in which the first link operates with a rotation of the third link, and an idling groove part positioned between the first and second operation groove parts. The idling groove part has the radius of curvature approximately equal to that of a locus pictured by the second pin between the first and second operation groove parts, and the idling groove part is set to approximately correspond to a timing where the first pin enters into the bent portion. Accordingly, the collision energy between the first pin and the side wall of the first cam groove can be readily made smaller without the shock absorbing mechanism, and the collision noise can be effectively reduced while the link mechanism is manufactured in low cost.